WASHINGTON — The eight senators who authored the newly unveiled bipartisan immigration reform bill said Thursday they are confident their efforts will not collapse the way a bipartisan gun control bill did this week.

Immigration reform has much wider support among both Democrats and Republicans, said Sen. Charles Schumer, D-N.Y. Schumer is one of the "Gang of Eight" senators who released their bill this week.

The other senators — who met 24 times over three months to craft their sweeping 800-plus-page bill — are Republican Sens. John McCain and Jeff Flake of Arizona, Lindsey Graham of South Carolina, Marco Rubio of Florida and Democratic Sens. Michael Bennet of Colorado, Dick Durbin of Illinois, and Bob Menendez of New Jersey.

"I think the majority of people in both caucuses really want to get this done," Schumer said at a Capitol Hill news conference. "I think this is ours to lose."

McCain said the most compelling reason for the senators' confidence is the unprecedented coalition of diverse interest groups that have come together around the legislation.

Among them: labor unions and the U.S. Chamber of Commerce, farmers and farm workers, Catholics and evangelical Protestants, and immigrant rights' advocates and conservatives such as Grover Norquist, president of Americans for Tax Reform. A bipartisan coalition of more than 30 state attorneys general also is calling on congressional leaders to pass reform.

"I never thought I'd be standing next to Richard Trumka," said McCain, chuckling as he turned to acknowledge the AFL-CIO president — one of more than 20 people standing behind the senators. "This is why we'll succeed."

The bill is slated to be marked up in the Senate Judiciary Committee in May following hearings on Friday and Monday. Senate Majority Leader Harry Reid, D-Nev., has promised to bring it to the floor for a vote by June.

The bill would increase border security, reform the visa system for legal immigrants, require employers to use an electronic database to ensure they hire workers who are in the country legally, and provide a pathway to citizenship for the estimated 11 million undocumented immigrants already here.

The bill's authors said they would welcome amendments from any of their Senate colleagues as long as those changes are not designed to kill the bill.

"I'm going to fight for this bill," Graham said. "If you've got a better idea, bring it on. But if you just want to kill it, then we're going to have to have a talk."

The senators said they know that the bill faces tough challenges in both the Senate and House because of the complexity and volatility of the issue.

Just before the bipartisan senators' spoke Thursday, a group of conservative Republicans was denouncing the bill in a separate press conference.

"We all want to solve this problem, not continue it, not perpetuate it, and certainly not grow it," Sen. David Vitter, R-La, said. "But we're fundamentally concerned that immediate amnesty with the promise of enforcement grows the problem."

Todd Garrison, sheriff of Dona Ana County in New Mexico, said the border is not secure and he's not convinced it will be before Congress grants legal status to those already in the country.

"It's hard to keep trust in our federal government on these issues," the sheriff said. "It's really frustrating."

But Flake said the bill is serious about border security. The bill requires the federal government to maintain a 90% annual effectiveness rate at apprehending and turning back illegal border-crossers in high-risk areas. High-risk border sectors are defined as areas where more than 30,000 people per year are apprehended.

"Arizona has borne the brunt of the federal government's unwillingness to secure our southern border, so I'm glad that this bill puts a priority on border security," Flake said.

Rubio took issue with fellow conservatives who denounce the bipartisan bill as "amnesty." He said the bill would put the undocumented immigrants already here on a path to earned citizenship that would require them to pay fines and taxes, learn English and American civics, and wait at least a decade to receive any of the government benefits available to citizens.

"It is not good for this country to have millions of people living in the shadows," Rubio said. "Leaving things the way they are — that's the real amnesty."

Durbin said the provision that was easiest for the eight senators to reach agreement on was the one that expedites the citizenship process for young immigrants who were brought to the United States as children. They would be able to get their "green cards" in five years and become citizens immediately after that.

"That was the shortest meeting we had," Durbin said.

Menendez, a longtime proponent of comprehensive immigration reform, said he had his doubts about his colleagues' commitment to the issue when their negotiations began three months ago. He said those doubts are now gone.

"This is one of the highest moments I've had in my 20 years in Congress," he said.

Bennet and other senators credited McCain and Schumer with providing the strong leadership that got the "Gang of Eight" through some tense negotiations.

"I want to thank my colleagues for showing me how the Senate can work," Bennet said.